The general purpose of this research is to elucidate the neural mechanisms by which the brain controls its own excitability so as to account for the periodic succession of states of consciousness: waking, sleeping, and dreaming. In particular, we aim to test the reciprocal interaction hypothesis of sleep cycle control to determine the cellular changes in the brain during sleep that result in the alternation of the sleeping and dreaming states. The reciprocal interaction hypothesis postulates that the sleep-dream cycle is the result of the contrapuntal oscillation of activity in two classes of brain stem neurons: the pontine reticular neurons (of which the prototype is the giant cell) and the biogenic amine-containing neurons (of which the prototypes are the noradrenergic locus coeruleus cell and the serotonergic dorsal raphe cell). The reciprocal interaction of these cell groups has been modeled and will be tested at four levels: anatomically, through autoradiographic methods; neurophysiologically, through single cell recording methods; neuropharmacologically, through drug micro-injection experiments; and, mathematically, through computer-aided system simulation and testing of fit with experimental data. Significance of the work is seen in its application to three scientific fields which are basic to psychiatry: the relationship of the brain to behavior; the pathophysiology of hallucinoid states; and, biological rhythms. We also believe that the approach taken may be useful in the study of other vegetative behaviors and in the development of rational treatment of sleep disorders.